1. Field of the Invention
The present invention generally relates to a decompression mechanism for an engine, and more particularly relates to an improved decompression mechanism that decompresses a combustion chamber of the engine when the engine is started.
2. Description of Related Art
Conventionally, in four stroke engines, a decompression mechanism is used to decompress a combustion chamber to ease cranking when a starting device starts the engine or to stop the engine. Typically, the decompression mechanism actuates an intake valve or an exhaust valve to open the valve at the beginning of the engine cylinder's compression stroke.
In prior engine designs, the decompression mechanism has been incorporated into a camshaft of the engine such that the decompression mechanism opens the until the rotational speed of the camshaft reaches generally a preset speed, at which time the decompression mechanism allows the valve to close. Typically, the decompression mechanism uses a centripetal force that increases when the rotational speed of the camshaft increases. For example, Japanese Patent Publication No. P2001-90516A, Japanese Utility Model Publication No. hei 06-10107 and Japanese Utility Model No. 2509668 disclose such decompression mechanisms. Generally, the decompression mechanism has a number of components and members. Thus, the decompression mechanism occupy a relatively large space.
The valves of the engine are usually disposed in a cylinder head of the engine. This valve arrangement is known as the OHV (overhead valve) mechanism. To actuate the valves, many engines use one or more camshafts, which in some designs are disposed in a crankcase of the engine below the cylinder head. Further, the engine can have two banks disposed in a V configuration. Because of this configuration, two camshafts are provided for the respective banks. The camshafts are inevitably placed close to each other because the camshafts are located at the bottom of the V configuration.
Due to such a close positioning, the engine can hardly provide an enough space to dispose the conventional decompression mechanism around the camshaft.